Ignore changes on target branch

When computing diff (for transient PR), consider only the changes
introduced by this PR.

Issue: ZENKO-5132

Author: francoisferrand

.github/actions/create-component-deployments/action.yaml

@@ -57,8 +57,14 @@ runs:
       id: filter
       shell: bash
       run: |
-        git fetch origin "${{ inputs.target-branch }}" --depth=1
-        git show "origin/${{ inputs.target-branch }}:${{ inputs.deps-file }}" > /tmp/base-deps.yaml 2>/dev/null || echo '{}' > /tmp/base-deps.yaml
+        # Diff against the merge-base (common ancestor with target branch) rather
+        # than the target branch tip, so deps where the PR branch is merely
+        # behind on target don't show up as "changed". Requires fetch-depth: 0
+        # on the caller checkout.
+        git fetch origin "${{ inputs.target-branch }}"
+        base_ref=$(git merge-base HEAD "origin/${{ inputs.target-branch }}")
+        echo "Diffing against merge-base $base_ref"
+        git show "$base_ref:${{ inputs.deps-file }}" > /tmp/base-deps.yaml 2>/dev/null || echo '{}' > /tmp/base-deps.yaml
 
         yq eval-all '
           select(fi == 0) as $curr | select(fi == 1) as $base |

.github/workflows/end2end.yaml

@@ -730,6 +730,9 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/checkout@v6
+        with:
+          fetch-depth: 0
+          filter: blob:none
       - name: Determine CI result
         id: result
         env:

tests/workflows/create-component-deployments.spec.ts

@@ -235,6 +235,62 @@ describe("create-component-deployments action", () => {
         expect(deployStep?.status).toBe(0);
     });
 
+    it("should ignore deps advanced on target branch after the feature branch was created", async () => {
+        // Simulate a stale feature branch: target branch moves on (backbeat bumped)
+        // while the feature branch only touches sorbet. Diff should be vs the
+        // merge-base, not the target tip, so backbeat must not be deployed.
+        nock("http://api.github.com").delete("/installation/token").reply(204).persist();
+
+        const repoPath = github.repo.getPath("zenko");
+        await exec(`git -C ${repoPath} checkout development/2.11`);
+        await exec(`yq -i '.backbeat.tag = "9.3.5"' ${repoPath}/solution/deps.yaml`);
+        await exec(`git -C ${repoPath} commit -m "bump backbeat on target" -- solution/deps.yaml`);
+        await exec(`git -C ${repoPath} push origin development/2.11`);
+        await exec(`git -C ${repoPath} checkout improvement/ZENKO-5210`);
+
+        act.setEnv("GITHUB_SHA", await getCommitHash());
+        act.setInput("target-branch", "development/2.11");
+
+        const result = await act.runEvent("workflow_dispatch", {
+            logFile: process.env.ACT_LOG ? path.join(__dirname, "act-delta-stale.log") : undefined,
+            mockApi: [
+                moctokit.rest.apps.getRepoInstallation().reply({
+                    status: 200,
+                    data: { id: 1, app_id: 12345, app_slug: "test-app" },
+                    repeat: 5,
+                }),
+                moctokit.rest.apps.createInstallationAccessToken().reply({
+                    status: 201,
+                    data: { token: "ghs_fake_token" },
+                    repeat: 5,
+                }),
+
+                // Only sorbet should be deployed (merge-base diff). Backbeat
+                // differs vs target tip but was not touched by the feature
+                // branch, so no mock for it.
+                moctokit.rest.repos.createDeployment({
+                    owner: "scality",
+                    repo: "sorbet",
+                    ref: "v1.2.2",
+                    ...commonDeploymentParams,
+                }).reply({ status: 201, data: { id: 101 } }),
+
+                moctokit.rest.repos.createDeploymentStatus({
+                    owner: "scality",
+                    repo: "sorbet",
+                    deployment_id: 101,
+                    state: "in_progress",
+                    log_url: "https://github.com/scality/zenko/actions/runs/1",
+                    description: "Zenko CI running",
+                }).reply({ status: 201, data: { id: 1 } }),
+            ],
+            bind: true,
+        });
+
+        expect(findStep(result, "Filter to changed dependencies")?.status).toBe(0);
+        expect(findStep(result, "Create or update deployments")?.status).toBe(0);
+    });
+
     it("should skip deployments when no deps changed", async () => {
         // Point to the same branch — no diff, so no components
         act.setInput("target-branch", "improvement/ZENKO-5210");